Plant growth-promoting rhizobacteria mediate induced systemic resistance in rice against bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae

Abstract

Seven Bacillus plant growth-promoting rhizobacteria spp. were evaluated for growth promotion and induced systemic resistance in rice against Xanthomonas oryzae pv. oryzae (Xoo). The identities of colonies of X. oryzae pv. oryzae grown on mXOS and PSA medium were confirmed by PCR employing specific primers TXTF and TXT4R. Among the seven strains tested as fresh suspensions, talc and sodium alginate formulations under laboratory and green house conditions, maximum germination of 86% was recorded after seed treatments with fresh suspension of Bacillus subtilis GBO3 followed by 85% germination treated with Bacillus pumilus SE34 in comparison to only 71% germination in the untreated controls. Similarly, the maximum vigor index of 1374 was obtained by seed treatment with fresh suspensions of B. subtilis strain GBO3 followed by treatments with strain SE34 with vigor index of 1323 in contrast to an index of only 834 observed in untreated controls. Among the treatments, seed treatments with fresh suspension of seven strains resulted in better germination and vigor assessments than talc based or sodium alginate formulations. Seed treatments with fresh suspension of strain SE34 gave 71% protection, followed by B. subtilis GBO3 and B. pumilus T4 with 58% and 52% protection, respectively, compared to the untreated controls. Seed treatments with talc based formulation of SE34 gave 66% protection, while GBO3 and T4 resulted in 52% and 50% protection, respectively, with similar formulation. Seed treatment with talc and sodium alginate formulations of strain SE34 gave 58% protection followed by GBO3 with 40% protection. Seed treatment with fresh suspensions of strains SE34 and GBO3 followed by challenge inoculations with Xoo increased accumulation of phenylalanine ammonia lyase, peroxidase and polyphenol oxidase compared to untreated control seedlings. Thus, the results of the present study suggest that the PGPR strains used as fresh suspensions and powdered formulations may have commercial potential in plant growth promotion and in management of rice bacterial leaf blight disease.